This invention relates to a liquid crystal display, and more particularly to a power supply for a liquid crystal display including a power source for delivering a voltage larger than the driving voltage of the display and a voltage regulator for adjusting the voltage applied to the display to the driving voltage for driving the display.
Liquid crystal displays are widely used for the display in electronic calculators, electronic cash registers (ECR), electronic timepieces and measuring instruments since the power consumption is considerably less than that of other types of display elements. Moreover, numerals, marks and figures can be easily displayed with a liquid crystal display element.
In the case of a ten digit-display for an electronic calculator, the liquid crystal display (field-effect type) consumes about 10 .mu.W (3 V). In contrast, a light emitting diode display consumes about 80 mW (3 to 5 V) and a fluorescent display tube consumes about 100 mW (24 V). Accordingly, the liquid crystal display is clearly superior in consumption of both power and voltage. Thus, the demand for liquid crystal displays is increasing when the liquid crystal display is utilized in combination with a C-MOS as a logic element for lower power consumption. Such electronic calculators are replacing electronic calculators employing conventional display elements for providing electronic calculators having extremely long battery life.
Notwithstanding the popularity of the liquid crystal display, there are difficulties in utilizing the liquid crystal display and many kinds of liquid crystal displays can not be used because of the following shortcomings. For example, the tolerance in the driving voltage for driving the display is narrow and more electrodes are required compared to other types of display elements since the liquid crystal display is not driven by a multiplex driving system, but is driven by the difference of the effective voltage between the lighting condition and the non-lighting condition. For example, when the driving voltage of a liquid crystal display is 3 V, the tolerance is .+-.5% or an absolute value of 0.15 V. The number of electrodes is 33 for driving a liquid crystal display in the 1/3 duty-driving method when the display includes 10 digits and each digit consists of 7 segments. In contrast, only 17 electrodes are required when a light emitting diode display is utilized. Accordingly, it would be desirable to provide a liquid crystal display which avoids the above noted inconveniences and additionally improves the usefulness of the liquid crystal display.